That mechanic works for me, although...DM said:How about this for a quick and dirty "starshell" rule?
Any ship with secondary armament may use 1 secondary AD to fire a starshell to any point within range (place a marker at the point where the starshell bursts). The starshell remains in place until the end of the turn; remove all markers in the end phase. Any ship within 6" of the marker counts as illuminated, +1 to incoming fire.
Also, any ship that is on fire is automatically spotted and has a +1 bonus for incoming fire.
I'm not sure what the ground scale is in VaS, but six inches might be a little large. That's a 12 inch diameter circle. How about a 3 or 4 inch radius from the "point of impact"?
I put something like the above in place for Grand Fleets.
The main difference is our rule set is hex-based (2000 yards per hex), and turns are 10 to 15 minutes. We say the effect lasts one turn, and illuminates ships in the one hex that's targeted.
It seems to work pretty well.
Kevin